1. Field of the Invention
The present invention relates to a resin multilayer substrate and a component module.
2. Description of the Related Art
A resin multilayer substrate is fabricated by stacking a single-sided copper clad sheet, a double-sided copper clad sheet, and the like.
WO2011/108308 discloses an example of a multilayer substrate incorporating components. WO2012/124421 discloses an example of a multilayer substrate having a surface on which components are mounted.
For producing a single-sided copper clad sheet or a double-sided copper clad sheet, a copper foil and a resin sheet are not bonded by chemical bonding such as an adhesive. Accordingly, the joining strength between the copper foil and the resin sheet is relatively weak. Therefore, there have been cases where the copper foil peeled off from the resin sheet by a certain trigger after completion of an assembly as a thermoplastic resin multilayer substrate. Accordingly, a problem can occur in the junction performance between the resin multilayer substrate and a mother substrate, and between the resin multilayer substrate and incorporated components or mounted components, and a problem could occur also in the reliability. Particularly, a copper foil arranged on the main surface of the resin multilayer substrate is exposed to the outside, which poses a problem that such a copper foil is relatively more likely to peel off.
In general, it is an anchor effect that mainly supports a junction between a copper foil and a resin sheet. For example, in the case where the surface of the copper foil is microscopically coarse to some extent at the junction surface, the anchor effect is achieved. However, for improving the electrical characteristics, the surface roughness of the copper foil will tend to decrease, so that it becomes difficult to achieve the anchor effect. Accordingly, it becomes necessary to improve the adhesion strength by a method other than that for increasing the joining strength by the anchor effect.
The “copper foil” used herein is not limited to a copper foil, but can be a metal foil in general.